Magnetic head

ABSTRACT

A magnetic head in which a pair of magnetic core halves each having a winding slot for placing a coil are abutted and unified to each other by thin magnetic metal films interposed in-between, and in which a magnetic gap is formed between abutting surfaces of the magnetic core halves. A bend is formed in the winding slot for bending the thin magnetic metal film at an acute angle when seen in cross-section. The magnetic head has a structure for prohibiting peeling of the thin magnetic metal film.

BACKGROUND OF THE INVENTION

This invention relates to a magnetic head in which a pair of magneticcore halves, each having a winding groove in which a coil is wound, areabutted and unified together via thin magnetic metal films and in whicha magnetic gap is defined between the abutting surfaces of the corehalves. More particularly, it relates to a magnetic head having astructure for prohibiting peeling of the thin magnetic metal films.

In a magnetic recording/reproducing apparatus, such as a video taperecorder (VTR) or a digital audio tape recorder (R-DAT), investigationsfor reducing the recording wavelength of information signals areproceeding with a view to improving the picture quality. In keeping uptherewith, a high-coercivity magnetic recording medium, such as aso-called metal tape employing magnetic metal powders as magneticpowders or an evaporation tape having a magnetic metal material directlydeposited on a base film, has come into use.

Investigations are also being conducted in the field of the magneticheads in connection with development of the high-coercivity magneticrecording medium. Thus, for coping with the high-coercivity magneticrecording medium, a magnetic head has been developed in which a magneticmetal material is used as a core material and the track width isreduced.

Such magnetic head is shown in FIG. 1, in which abutment surfaces of apair of magnetic cope halves 101, 102, formed of magnetic oxides, suchas Mn-Zn ferrite, are partially removed for forming surfaces for formingthin magnetic metal films, and thin magnetic metal films 105, 106,formed e.g., of sendust, are formed on these forming surfaces by thevacuum thin film forming technique. These thin magnetic metal films 105,106 are abutted to each other for forming a magnetic gap 107. A slidecontact surface for a magnetic tape is formed in a track width controlgroove and a low-melting glass or high-melting glass 108 is charged inthe track width control groove for prohibiting abrasion of the thinmagnetic metal films 105, 106.

On the abutting surfaces of the magnetic core halves 101, 102, there isformed a winding slot 109 for placing a coil therein and for controllingthe depth d of a magnetic gap 107. The winding slot 109 is comprised ofan upper inclined portion 109a for controlling the depth d of themagnetic gap 107 and a bottom 109b having a value of Rmax approximately0.2 μm by toughening. The winding slot 109 encompasses not only the solewindow type in which the slot is formed in only one of the magnetic corehalves but also the dual window type in which the slot is formed in eachof the magnetic core halves 101, 102.

For producing this sort of the magnetic head, a pair of core blocks arefabricated through a process including a step of forming grooves in asubstrate of a magnetic oxide and forming a thin magnetic metal film, astep of charging fused glass 108 and machining the surface to a mirrorfinish. These core blocks are abutted together to form a unified blockwhich is sliced into magnetic head chips and a coil is placed in each ofthe magnetic chips.

In abutting the magnetic core halves, on each of which a thin magneticmetal film is formed, for unifying these core halves, there is produceda force of stress at the time of forming these films 105, 106 andthermal stress induced when charging the fused glass in the track widthcontrol groove thus lowering adhesion in an interface between the films105, 106 and the ferrite. The result is that the thin magnetic metalfilm tends to be peeled during the subsequent step of chip slicing andcoil winding.

For overcoming this inconvenience, it may be contemplated to usespecific shapes of the inclined section 109a of the winding slot 109controlling the depth of the magnetic gap 107, or to charge the fusedglass as far as a winding section 109c of the winding slot 109, as shownin FIG. 2. However, this may lead to difficulties in placing the coil inthe slot in the subsequent coil winding step.

OBJECT AND SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a magnetichead in which the force of stress incurred during formation of the thinmagnetic metal film is relaxed to prevent peeling of the magnetic tinfilms interposed between magnetic core halves as well as to eliminateany adverse effects on magnetic characteristics of the magnetic head.

According to the present invention, there is provided a magnetic head inwhich a pair of magnetic core halves, each having a winding slot forplacing a coil therein, are abutted and unified to each other by thinmagnetic metal films interposed in-between, and in which a magnetic gapis formed between abutting surfaces of the magnetic core halves. A bendis formed in the winding slot for bending the thin magnetic metal filmat an acute angle when seen in cross-section.

If the angle of the bend is a right angle or an obtuse angle, the forceof stress incurred during formation of the thin magnetic metal filmcannot be effectively relaxed, while the peeling of the thin magneticmetal film incurred during the production process of the magnetic headbecomes continuous, so that effective peeling prevention cannot beachieved.

Such bend may be provided in the winding slot formed in each of themagnetic core halves.

According to the present invention, since the thin magnetic core halvesare bent at an acute angle, the force of stress incurred duringformation of the thin magnetic metal films and during charging of thefused glass in the track width control groove is relaxed withoutoperating continuously in a pre-set direction, thus improving adhesionof the thin magnetic metal films.

On the other hand, if peeling of the thin magnetic metal film isincurred at one of the sides defining the acute angle, such peeling isfractionated at the bend of the acute angle without affecting theopposite side, so that the effect of peeling is isolated from thevicinity of the magnetic gap without deteriorating the performance ofthe magnetic head.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing an illustrative conventionalmagnetic head.

FIG. 2 is a perspective view showing another illustrative conventionalmagnetic head.

FIG. 3 is a perspective view showing an embodiment of a magnetic headaccording to the present invention.

FIG. 4 is a schematic front view showing the shape of a winding slot ofthe magnetic head shown in FIG. 3.

FIG. 5 is a perspective view showing a modified embodiment of a magnetichead according to the invention, with one of the magnetic core halfsides removed.

FIG. 6 is a schematic front view showing the shape of a winding slot ofthe magnetic head shown in FIG. 5.

FIG. 7 is a perspective view showing a step of forming a magnetic metalfilm forming surface on a block substrate in the production process forthe magnetic head shown in FIG. 5.

FIG. 8 is a perspective view showing a step of forming a winding slot ona substrate for superposition in the production process for the magnetichead shown in FIG. 5.

FIG. 9 is a perspective view showing a step of forming a first cutgroove in the production process for the magnetic head shown in FIG. 5.

FIG. 10 is a perspective view showing a step of superimposing asubstrate for superposition on a block substrate for fabricating acombined block in the production process for the magnetic head shown inFIG. 5.

FIG. 11 is a perspective view showing a step of cutting the unifiedblock combined from the substrate and the block substrate withinterposition of the fused glass in the production process for themagnetic head shown in FIG. 5.

FIG. 12 is a perspective view showing a step of placing a coil in themagnetic head for fabricating a magnetic head device in the productionprocess for the magnetic head shown in FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, preferred embodiments of a magnetic headaccording to the present invention will be explained in detail.

The magnetic head of the present embodiment is prepared by combining apair of magnetic cores 2, 3 by abutting and bonding thin magnetic metalfilms 4, 5 deposited on abutting surfaces 2a, 3a thereof to each otherand by forming a magnetic gap g operating as a recording/reproducing gapon the abutting surfaces 2a, 3a, as shown in FIGS. 3 and 5. FIG. 5 showsa single window type magnetic head embodying the present invention.

The magnetic cores 2, 3 are formed of a magnetic oxide, such as Mn-Znbased ferrite. A winding slot 6 for placing a coil C therein and forcontrolling the depth d of the magnetic gap g is formed on the abuttingsurfaces 2a, 3a of the magnetic cores 2,

In the instant embodiment, a surface 6b of the bottom of the windingslot 6 is a toughened surface with the surface roughness being on theorder of 5 μm in terms of the maximum height Rmax prescribed in JIS B0601. By forming the surface 6a as the toughened surface, part of thethin magnetic metal films 4, 5 is affixed to the toughened surface thusrealizing a highly efficient head structure which is high in adhesionand mechanical strength and in which the pseudo-gap from the connectingportion between the ferrite and the thin magnetic metal films 4, 5 issubstantially negligible. In addition, the magnetic head may befabricated highly efficiently and accurately by the production processwhich will be explained subsequently.

In particular, with the magnetic head 1 of the instant embodiment, bentportions 11, 11 for bending the thin magnetic metal films 4, 5 at anacute angle are formed at an inclined section 6a of the winding slot 6.These bends 11, 11 operate for prohibiting the peeling of the thinmagnetic metal films 4, 5. When seen in the vertical cross-sectionalview of FIG. 4, each bent portion 11 includes an acute angle θ2 betweensides X and Y facing the abutting surfaces 2a, 3a of the magnetic corehalves 2, 3.

With the magnetic head 1 of the instant embodiment, protrusions 12, 12are formed in continuation to the bent portions 11, 11, as shown in FIG.4.

The bent portions 11, 11 are formed in the inclined section 6a of thewinding slot 6. The angle θ1 of the inclined section 6a is preferably20° to 70° with respect to the depth d of the magnetic gap g.

The bent portions 11, 11 are sized so that a height H1 associated withthe side X is 0.1 to 0.3 mm and a height H2 associated with the side Yis 0.01 to 0.1 mm.

If the angle θ2 of the bends 11, 11 is an obtuse angle or a right angle,the force of stress induced during formation of the thin magnetic metalfilms 4, 5 is not continuous and cannot be relaxed. In addition, peelingof the thin magnetic metal films 4, 5 incurred during the productionprocess of the magnetic head 1 becomes continuous so that effectivepeeling prevention cannot be achieved.

Conversely, if the angle θ2 of the bends 11, 11 is an acute angle, theforce of stress is fractionated. On the other hand, if the peeling ofthe thin magnetic metal films 4, 5 is incurred only at the side Y on oneside of the acute angle θ2, the flow of peeling of the thin magneticmetal films 4, 5 is fractionated at the bend 11 so that the oppositeside X is not affected by the peeling. Thus the vicinity of the magneticgap g, which represents a crucial portion in producing the playbackoutput, is not affected by the peeling, thus prohibiting deteriorationin the performance of the magnetic head. In addition, the thin magneticmetal films 4, 5 may be further improved in adhesion, in conjunctionwith the favorable effect of the toughened surface 6b of the bottom ofthe winding slot 6, thus improving mechanical strength.

On the other hand, the protrusions 12, 12, operating for prohibitingpeeling of the thin magnetic metal films 4, 5, also operate forprohibiting flow of the fused glass 7.

The lateral sides of the magnetic cores 2, 3, facing the winding slot 6,are formed with winding guide grooves 8, 9 for improving the windingstate of the coil C placed in the winding slot 9.

The magnetic cores 2, 3, with the thin magnetic metal films 4, 5interposed in-between, are bonded together by fused glass 7, and themagnetic gap g, operating as a recording/reproducing gap, is formed inthe abutting surfaces 2a, 3a.

As the magnetic metal materials, employed in the instant embodiment,magnetic amorphous alloys, or so-called amorphous alloys, sendust, whichis an Fe-Al-Si based alloy, an Fe-Al-Si based alloy, an Fe-Al basedalloy, an Fe-Ni based alloy, an Fe-Si based alloy, an Fe-Ga-Si basedalloy, a Ga-Si-Ru based alloy or permalloy, may be employed. Theamorphous alloys may be enumerated by metal-metalloid based amorphousalloys, such as alloys composed of one or more of elements Fe, Ni and Coand one or more of elements P, C, B and Si, or alloys mainly composed ofthe above alloys and also containing Al, Ge, Be, Sn, In, Mo, W, Ti, Mn,Cr, Zr, Hf and Nb, and metal-metal-based amorphous alloys, mainlycomposed of transition elements, such as Co, Hf or Zr or rare-earthelements. The magnetic metal material may be deposited as films byvacuum thin film forming techniques, such as flash evaporation, vacuumevaporation, ion plating, sputtering or cluster ion beaming.

The method for producing the magnetic head is explained with referenceto production of the so-called single-window magnetic head in which onlyone of the magnetic core halves 2, 3 has the winding slot 6. However,the present invention is applicable to the so-called double windowmagnetic head having winding slots in both the magnetic core halves 2,3.

For fabricating the magnetic head according to the present invention, aparallelopiped-shaped block substrate 21 of e.g., Mn-Zn ferritematerial, and a block for superposition 22, that is a block to besuperposed on the block substrate, as shown in FIGS. 7 and 8,respectively, are prepared. These substrates are dimensioned so that thesides a, b and c are equal to 30 mm, 1 mm and 2 mm, respectively. Anupper surface 21a of the block substrate 21 is a surface proving to bean abutment surface 2a or 3a of the magnetic gap g. On this surface 21ais formed a first groove 23 by e.g., a metal grindstone #4000 so as tobe parallel to the side a. Using a metal grindstone having a distal endof 90°, a metal film forming surface 20, inclined at an angle θ4 of 45°with respect to the magnetic gap g, was formed.

Then, as shown in FIG. 8, a winding slot 6, as a second groove, wasformed on the opposite side block, that is the block for superposition22, using e.g., a metal grindstone #600. In the instant embodiment, thewinding slot 6 was machined so that the distal end on the order of 0.04μm is left from the center of the winding slot 6.

That is, the angle θ1 of the inclined section 6a of the winding slot 6was formed so as to be 20° to 70° with respect to the depth d of themagnetic gap g. The bend 11 and the protrusion 12 contiguous to the bend11 were then formed in the inclined section 6a of the winding slot 6designed to control the depth d of the magnetic gap g. The bend 11 andthe protrusion 12 were formed so as to have acute angles incross-section. That is, the height H1 for the side X was set to 0.1 mmto 0.3 mm, while the height H2 for the side Y was set to 0.01 mm to 0.1mm.

A track width control groove 24 was then formed in the block forsuperposition 22, as shown in FIG. 9. In the present embodiment, thetrack width was set to 21 μm. The angle θ4 of the track width controlgroove was set to 10° to 80°. Although a vee-shaped track width isproduced using e.g., the metal grindstone, it may also be in a U-shape.

After machining the surface which proves to be an abutment surface forthe magnetic gap g of the block substrate 21 to a mirror finish, a thinmagnetic metal film 25 of a sendust or the like alloy is formed by avacuum thin film forming technique, such as sputtering, in a groove 23inclusive of a metal film forming surface 21b.

In the instant embodiment, the thin magnetic metal film 25 is formed forextending to the winding slot 6. However, a ZrO₂ film, films of metals,such as Cr, Al, Si or Pt, or alloys thereof, or a laminated film ofthese metal or alloy films, may also be employed in place of the SiO₂film.

The thickness of the thin magnetic metal film 25 was set to 3 to 6 μm,that is one-half the width g of the effective magnetic gap g, forimproving high frequency characteristics.

The block substrate 21 and the block for superposition 22, produced bythe above process, were placed side-by-side so that the magnetic metalmaterial constituting the track width will be abutted to each other withhigh precision, as shown in FIG. 10. The blocks 21, 22 are then bondedto each other for producing a unified block 31. Such bonding is effectedby charging fused glass 7 into the first groove 23 of each core and inthe winding slot 6. That is, a bar-shaped glass is placed in the windingslot 6 and thermally processed so that fused glass will flow into theinside of the inclined section 6a. In this case, any thermal stressinduced during charging of the fused glass into the track width controlgroove 24 is relaxed by the bent portion 11.

The unified block 31 is then sliced along lines B and B', centered aboutan area of abutment of the thin magnetic metal film 25 of the trackwidth T. An area surrounded by lines C and C', corresponding to thewidth of the surface of the resulting magnetic head chip which proves tobe a surface on which slides the magnetic recording medium, is machinedto form a recess or step for assuring that the magnetic recording mediumis engaged with the recess or step. If an azimuth angle is required, theunified block is sliced with a pre-set azimuth angle.

The portion of the resulting magnetic head chip which proves to be thesurface on which slides the magnetic recording medium, is ground to acylindrical finish for completing the magnetic head 1 as shown in FIG.5.

The coil C is placed around the magnetic head 1, thus produced, forfabricating a magnetic head device 10.

The magnetic head thus produced differs from the conventional head inthat the thin magnetic metal films 4, 5 are not peeled during theproduction process, in particular the chip slicing and coil windingsteps. In addition, magnetic characteristics of the magnetic head 1 arenot affected adversely.

The reason is that, with the magnetic head 1 of the illustratedembodiment, the force of stress induced during formation of the thinmagnetic metal films 4, 5 is not continued but fractionated across thesides X and Y due to the bend 11 configured for bending the thinmagnetic metal films 4, 5, and that flow of peeling of the thin magneticmetal films 4, 5, occasionally incurred at e.g. the side Y of the acuteangle θ2, is fractionated at the bend 11 without reaching the oppositeside X, thus prohibiting the vicinity of the magnetic gap g from beingaffected by the peeling. If the angle θ2 of the bend 11 is a right angleor an acute angle, the peeling of the thin magnetic metal films 4, 5produced during the production process of the magnetic head 1 iscontinued over the bend 11 so that effecting prevention of the peelingcannot be achieved. Since the protrusion 12 is formed in continuation tothe bend 11, the fused glass 7 may be prevented effectively from flowingtowards the winding section 6c.

The present invention may be applied to any magnetic head provided withthe thin magnetic metal films 4, 5. That is, the present invention maybe applied to a so-called metal-in-gap type magnetic head in which thethin magnetic metal films 4, 5 are formed parallel to the magnetic gapforming surface, or to a so-called laminated magnetic head in which thinmagnetic metal films are sandwiched between substrates of non-magneticmaterial to constitute magnetic core halves which are abutted to eachother and unified by glass fusion.

What is claimed is:
 1. A magnetic head in which a pair of magnetic corehalves, each having a winding slot for placing a coil therein, andfacing and unified to each other by thin magnetic metal films interposedin-between, and in which a magnetic gap is formed between facingsurfaces of the magnetic core halves, wherein the improvementcomprises:said winding slots having opposing sidewalls each partiallyoverlaid by one of said magnetic metal films, said sidewalls each havinga bend formed for bending said thin magnetic metal film into an acuteangle when seen in cross-section in a plane perpendicular to a trackwidth direction of said magnetic gap.
 2. The magnetic head as claimed inclaim 1 wherein a protrusion contiguous to said bend is formed in thewinding slot of at least one of the magnetic core halves.
 3. Themagnetic head as claimed in claim 1 wherein said bend is formed in thewinding slot of each of the magnetic core halves.
 4. The magnetic headas claimed in claim 1 wherein said bend is formed in an inclined sectionof the winding slot configured for controlling the depth of the magneticgap.
 5. The magnetic head as claimed in claim 1 wherein the angle ofinclination of the inclined section of the winding slot is 20° to 70°with respect to the depth of the magnetic gap.
 6. The magnetic head asclaimed in claim 2 wherein said protrusion has an acute apex angle whenseen in a cross-section.
 7. The magnetic head as claimed in claim 1wherein said protrusion is formed in the winding slot formed in each ofthe magnetic core halves.
 8. A magnetic head having a pair of magneticcore halves, and a winding slot for placing a coil therein, said corehalves facing and unified to each other, having thin magnetic metalfilms interposed in-between, and in which a magnetic gap is formedbetween facing surfaces of the magnetic core halves, the improvementcomprising:said winding slot having opposing sidewalls each partiallyoverlaid by one of said magnetic films, one of said sidewalls having abend for bending one of said thin magnetic metal films into an acuteangle when seen in cross-section in a plane perpendicular to a trackwidth direction of said magnetic gap.
 9. The magnetic head as claimed inclaim 8 further comprising a protrusion contiguous to said bend andextending into said winding slot.
 10. The magnetic head as claimed inclaim 8 wherein said respective other sidewall also comprises a bend forbending a respective other of said thin magnetic metal films into anacute angle when seen in cross-section in said plane perpendicular tosaid track width direction of said magnetic gap.
 11. The magnetic headas claimed in claim 10 further comprising a protrusion formed on each ofsaid sidewalls facing inwardly and each protrusion contiguous to one ofsaid bends, said protrusions comprising cantilever ridges extending intosaid winding slot from said sidewalls.
 12. The magnetic head as claimedin claim 11 wherein said protrusions each have an acute apex angle whenseen in said cross-section.
 13. The magnetic head according to claim 8wherein said bend is formed on an inclined section of said sidewall. 14.A magnetic head as claimed in claim 13 wherein an angle of inclinationof the inclined section of said wall is 20° to 70° with respect to adepth direction of the magnetic gap.